Amorphous Oxide TFT with Controlled Carrier Concentration
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Solution Overview
Problem
Thin film field effect transistors using amorphous oxide semiconductors face challenges in achieving low OFF current and high ON-OFF ratio, particularly when operated on flexible resin substrates, as they tend to have low electron mobility and are sensitive to environmental temperature variations, leading to performance instability.
Innovation Solution
A thin film field effect transistor design with an active layer made of amorphous oxide semiconductor having a carrier concentration of 3 × 10^17 cm^-3 or more and a film thickness of 0.5 nm to 10 nm, combined with a low carrier concentration layer, is used, which includes In, Ga, and Zn, and is fabricated on a flexible resin substrate to maintain stability and performance across varying temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous oxide semiconductor is used in active layer to form film at low temperature on resin substrate, then ease of manufacture is improved, but OFF current becomes high and ON-OFF ratio becomes low
Solution Approach 1:
The invention changes the carrier concentration parameter of the amorphous oxide semiconductor from conventional high values (10^18-10^20 cm^-3) to a specific low range (10^16 to less than 10^18 cm^-3). This parameter change enables the material to simultaneously achieve low OFF current (10^-21 to 10^-24 A) and high ON-OFF ratio (10^8 to 10^11), while maintaining the ability to form films at low temperatures on resin substrates.
2Reliability
If carrier concentration of amorphous oxide semiconductor is reduced to less than 10^18 cm^-3 to lower OFF current, then OFF current is reduced, but temperature stability and performance consistency deteriorate
Solution Approach 1:
The invention optimizes the carrier concentration to a specific range (10^16 to less than 10^18 cm^-3) rather than simply reducing it. This precise parameter control, combined with specifying the active layer thickness (0.5 nm to 10 nm), achieves both low OFF current and improved temperature stability, as the controlled carrier concentration reduces sensitivity to environmental variations.
Solution Approach 2:
The invention adds the dimension of film thickness control (0.5 nm to 10 nm) to the carrier concentration parameter. This dual-parameter approach (carrier concentration + thickness) enables simultaneous optimization of multiple performance characteristics including OFF current, temperature stability, and mobility, which cannot be achieved by carrier concentration alone.
3Reliability
If silicon thin film is used for active layer to achieve stable performance, then reliability is improved, but thermal treatment at high temperature is required which is incompatible with resin substrate
Solution Approach 1:
The invention changes the material parameter from silicon-based semiconductors to amorphous oxide semiconductors with specifically controlled carrier concentration (10^16 to less than 10^18 cm^-3). This material substitution enables film formation at low temperatures on resin substrates while achieving performance stability comparable to or exceeding silicon-based devices, eliminating the need for high-temperature thermal treatment.
Data Source
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AI summary
A TFT is provided which includes, on a substrate, at least a gate electrode, a gate insulating layer, an active layer containing an amorphous oxide semiconductor, a source electrode, and a drain electrode, wherein a carrier concentration of the active layer is 3 × 1017 cm-3 or more and a film thickness of the active layer is 0.5 nm or more and less than 10 nm. A TFT is provided which has a low OFF current and a high ON-OFF ratio, and is improved in environmental temperature dependency. Also, a display using the TFT is provided.